LeetCode in Kotlin
590. N-ary Tree Postorder Traversal
Easy
Given the root of an n-ary tree, return the postorder traversal of its nodes’ values.
Nary-Tree input serialization is represented in their level order traversal. Each group of children is separated by the null value (See examples)
Example 1:
Input: root = [1,null,3,2,4,null,5,6]
Output: [5,6,3,2,4,1]
Example 2:
Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: [2,6,14,11,7,3,12,8,4,13,9,10,5,1]
Constraints:
- The number of nodes in the tree is in the range
[0, 104]. 0 <= Node.val <= 104- The height of the n-ary tree is less than or equal to
1000.
Follow up: Recursive solution is trivial, could you do it iteratively?
Solution
import com_github_leetcode.Node
/*
* Definition for a Node.
* class Node(var `val`: Int) {
* var children: List<Node?> = listOf()
* }
*/
class Solution {
private var ans: ArrayList<Int>? = null
fun postorder(root: Node?): List<Int> {
ans = ArrayList()
recursion(root)
if (root != null) {
ans!!.add(root.`val`)
}
return ans as ArrayList<Int>
}
private fun recursion(root: Node?) {
if (root == null) {
return
}
for (child in root.neighbors) {
recursion(child)
ans!!.add(child.`val`)
}
}
}